Fixed code style issue

Author: sidolov

app/code/Magento/Backend/Block/Widget/Grid/Massaction/AbstractMassaction.php

@@ -215,7 +215,7 @@ public function getGridJsObjectName()
 
     /**
      * Retrieve JSON string of selected checkboxes
-     * 
+     *
      * @return string
      * @SuppressWarnings(PHPMD.RequestAwareBlockMethod)
      */